Add batch_id-with-timestamp compound index to message store models.
Fix migration tests.
New migrations for v2 message store models.
Message store query methods for the new timestamped compound indexes.
Merge branch 'develop' into feature/issue-864-message-store-compound-index
Merge branch 'develop' into feature/issue-864-message-store-compound-index
Merge branch 'develop' into feature/issue-864-message-store-compound-index
Merge branch 'develop' into feature/issue-864-message-store-compound-index
Merge branch 'feature/issue-864-message-store-compound-index' into develop